The secondary biochemical effluent of a sewage treatment plant generally still has a certain concentration of pollutants such as nitrogen, phosphorus and suspended matters, which makes a great threat to the eco-environment and human beings; and in recent years China continuously improves the discharge standard of municipal sewage, and different regions also successively issue a series of planning and policies of energy saving and emission reduction. Therefore, it is of extremely urgent to upgrade and reconstruct the existing sewage treatment plant.
A denitrification biological nitrogen removal apparatus is widely applied in sewage deep-denitrification due to its advantages such as small footprint, convenient running management, and great processing effect. The working principle of the apparatus is that, when the sewage flows through a filtering material contained within the filter, a biomembrane adhered on the filtering material reduces nitrite and nitrate into nitrogen gas under an anaerobic condition; and meanwhile under the physical interception and absorption actions of the filtering material, the suspended solids contained in the inlet water are also removed. The COD (chemical oxygen demand) of the secondary biochemical effluent is generally low, but the denitrifying bacteria needs to consume the COD for nitrogen removal, and thus it needs to additionally add an externally added carbon source, which increases the running cost; furthermore the effluent of the secondary sedimentation tank often contains a certain concentration of DO, and thus due to the presence of DO and the carbon source, it will result in reproduction of heterotrophic bacteria on the surface of the filtering material of the filter bed, and under the coaction of the heterotrophic bacteria and the suspended solids, the surface layer of the filtering material is liable to be clogged and thus the processing effect is influenced.
To ensure the processing effect and reduce the running cost, currently most solving methods often start with precise control of externally added carbon sources and real-time automatic backwash, and for example Chinese patent No. 201410140512.8, which is published at Apr. 9, 2014, discloses a patent application document named “Intelligent and Precise Carbon-Source Dosing System for Denitrification Deep-Bed Filter”, the invention disclosed in the document relates to an intelligent and precise carbon-source dosing system for a denitrification deep-bed filter, which is provided with a water inlet, a COD inlet water detector, a dosing meter pump, an inlet water meter pump, a central control system, a dissolved oxygen meter, a pH meter, a thermometer, a denitrification deep-bed filter, a COD outlet water detector, a water outlet, and a nitrate analyzer of the water outlet and inlet, wherein the carbon-source dosage is controlled through the central control system according to the collected COD, flow rate, DO, temperature and pH value signal. Chinese patent No. 201110022603.8, which is published at Jul. 4, 2012, discloses a patent application document named “Real-Time Automatic Backwash Control System for Denitrification Filter and Method for Operaing the Same”, the invention disclosed in the document relates to a real-time automatic backwash control system for denitrification filter and a method for operating the same, the system is provided with an on-line turbidity sensor, a nitrate sensor and a turbidity detector, and a nitrate detector arranged in the denitrification filter, and is also provided with a process controller and an industrial computer; the invention also, relates to a method for operating the backwash control system, which includes steps of: 1. starting of the control system; 2. parameter processing and determining; 3. water discharging process; 4. gas-only backwashing; 5. gas-water combined backwashing; and 6. water-only backwashing. For these patents, the cost is reduced by optimizing the dosage of the externally added carbon source, and the filter is backwashed in real time to ensure the processing effect of the filter, but the pollutant carrying capacity of the filter itself is not increased and the influence of DO on the processing effect of the filter is not reduced, and thus problems such as high running cost and complex operation.